This invention relates to communication systems with satellite communication channels providing links among a plurality of earth stations.
Communication systems utilize satellites in different types of orbits. Satellites in a geostationary orbit (GSO) offer advantages as appearing to be stationary relative to a location on the earth. This enables the antennas on the earth stations to be aimed at the GSO satellite using a simple tracking system. Other communication systems utilize satellites having a low earth orbit (LEO) or a medium earth orbit (MEO). Because satellites in these systems are moving relative to corresponding earth stations, tracking of the position of a satellite as it moves through the field of view of the earth station is required. Additionally, as one satellite goes out of range of a particular earth station, communications must be handed off to another satellite coming into the field of view of the earth station.
Existing GSO satellites typically operating in the C band (about 3-7 GHz) or in the Ku band (about to 10-15 GHz) are used for trunking and very small aperture terminal (VSAT) applications. These satellites typically have 24 duplex transponders each with a 36 MHz bandwidth for up and down links, with each transponder supporting approximately 45 Mbps of data traffic. Thus, the data traffic capacity of each satellite is approximately 1 Gbps. Additionally, the beams from such satellites are fixed and are thus unable to allocate payload resources on an as needed basis. Commercial Ka band (17.7-30 GHz) satellites support VSAT applications. The data handling capacities and limited flexibility of transponders utilized by such Ka-band satellites are not well-suited to embrace the increasing demands for high data communications.